Methyl ester biodiesel production

Biodiesel (fatty acid methyl ester (FAME)) production is based on transesterification of vegetable oils and fats through the addition of methanol (or other alcohols) and a catalyst, giving glycerol as a by-product (which can be used for cosmetics, medicines and food). Oil-seed crops include rapeseeds, sunflower seeds, soy beans and palm oil seeds, from which the oil is extracted chemically or mechanically. Biodiesel can be used in 5%-20% blends with conventional diesel, or even in pure form, which requires slight modifications in the vehicle. 

Standard canola oil, mainly because of its fatty acid composition, is relatively well suited for biodiesel production. Harrington (145), and Knothe et al. (146) discussed desired properties of fatty acid ester structure for biodiesel. Knothe et al. (146) also discussed biodiesel standards in different countries, for those interested. Briefly, the desired properties of vegetable oil fatty acids for methyl ester biodiesel can be summarized as follows ... 

In the enzymatic process utilized for the production of fatty acid methyl ester (biodiesel) from rapeseed oil, several factors can influence both the yield and rate. These factors include the reaction solvent, reaction temperature, reaction time, methanol/oil molar ratio, enzyme amount, and water content [7, 9, 12-14]. The initial step of this study involved the identification of factors likely to influence the conversion. 

TDSP Procedure for Production of Methyl Ester Biodiesel. 

As a result of transesterification process, a mixture of fatty acid methyl esters (biodiesel) and glycerol are obtained. These products are in different phases and can be separated by gravitational settling (Figure 2). 

Experiments showed that high methyl ester yields can be achieved with solid bases and super acids under moderate reaction conditions. The solid bases were more effective catalysts than the solid super acids. High stability can be achieved by an ordinary inexpensive preparation process, and the catalyst can be separated easily from the reaction products in the heterogeneous catalysis process. The costly catalyst removal process can be avoided compared with the homogeneous process. Therefore, the heterogeneous process using a solid catalyst should be more economical for biodiesel production. 

The traditional catalyst used for esterification of acids to methyl esters is sulfuric acid. Homogeneous sulfuric acid catalysis has many downsides. When using sulfuric acid, much capital expense is required for Hastalloy and/or other specialty metals of construction. Homogeneous catalysis results in the contamination of the product by sulfur containing species. Therefore, neutralization and removal of acid is required to meet biodiesel specifications and to protect the downstream transesterification reactor. Inevitably, when using sulfuric acid, organic sulfur compounds will be produced. These products will cause the resultant biodiesel to fail specification tests. 

Biodiesel is a mixture of methyl esters of fatty acids and is produced from vegetable oils by transesterification with methanol (Fig. 10.1). For every three moles of methyl esters one mole of glycerol is produced as a by-product, which is roughly 10 wt.% of the total product. Transesterification is usually catalyzed with base catalysts but there are also processes with acid catalysts. The base catalysts are the hydroxides and alkoxides of alkaline and alkaline earth metals. The acid catalysts are hydrochloride, sulfuric or sulfonic acid. Some metal-based catalysts can also be exploited, such as titanium alcoholates or oxides of tin, magnesium and zinc. All these catalyst acts as homogeneous catalysts and need to be removed from the product [16, 17]. The advantages of biodiesel as fuel are transportability, heat content (80% of diesel fuel), ready availability and renewability. The... 

The process involves reacting the degummed oil with an excess of methyl alcohol in the presence of an alkaline catalyst such as sodium or potassium methoxide, reaction products between sodium or potassium hydroxide and methyl alcohol. The reaction is carried out at approximately 150°F under pressure of 20 psi and continues until trans-esterification is complete. Glycerol, free fatty acids and unreacted methyl alcohol are separated from the methyl ester product. The methyl ester is purified by removal of residual methyl alcohol and any other low-boiling-point compounds before its use as biodiesel fuel. From 7.3 lb of soybean oil, 1 gallon of biodiesel fuel can be produced. See FIGURE 12-5. 

Biodiesel is made through a ohemioal prooess called transesterification, whereby the glyoerin is separated from the fat or vegetable oil. The process leaves behind two products methyl esters (the chemical name for biodiesel) and glyoerin (a valuable byproduct usually used in soaps and other products). 

Biodiesel A fuel derived when glycerin is separated from vegetable oils or animal fats. The resulting byproducts are methyl esters (the chemical name for biodiesel) and glycerin which can be used in soaps and cleaning products. It has lower emissions than petroleum diesel and is currently used as an additive to that fuel since it helps with lubricity. 

In homogeneous catalysis, the catalyst is in the same phase as the reactants and products. Here we will concentrate on homogeneous catalysis in the liquid phase. In the classic case, the reactant (also called the substrate) molecules and the catalyst are reacted in a solvent. For example, the transesterification of fatty acid triglycerides with methanol (Figure 1.10) is catalyzed by hydroxide (OH-) ions. This is an important process for making fatty acid methyl esters which are then used as biodiesel. 

Fatty acid methyl esters (FAMEs) show large potential applications as diesel substitutes, also known as biodiesel fuel. Biodiesel fuel as renewable energy is an alternative that can reduce energy dependence on petroleum as well as air pollution. Several processes for the production of biodiesel fuel have been developed. Transesterification processes under alkali catalysis with short-chain alcohols give high yields of methyl esters in short reaction times. We investigated transesterification of rapeseed oil to produce the FAMEs. Experimental reaction conditions were molar ratio of oil to alcohol, concentration of catalyst, type of catalyst, reaction time, and temperature. The conversion ratio of rapeseed oil was enhanced by the alcohohoil mixing ratio and the reaction temperature. 

Reaction temperature and time were significant operating parameters, which are closely related to the energy costs, of the biodiesel production process. Figure 7 shows the effect of reaction time on the transesterification of rapeseed oil at a catalyst concentration of 1%, molar ratio of 1 6, and 60°C. Within 5 min, the reaction was rapid. Rapeseed oil was converted to above 85% within 5 min and reached equilibrium state after about 10 min. Several researchers reported that the conversion of vegetable oils to FAME was achieved above 80% within 5 min with a sufficient molar ratio (8,11). For a reaction time of 60 min, linoleic acid methyl ester was produced at a low conversion rate, whereas oleic and linolenic methyl ester were rapidly produced. 

Biodiesel fuel was prepared by a two-step reaction hydrolysis and methyl esterification. Hydrolysis was carried out at a subcritical state of water to obtain fatty acids from triglycerides of rapeseed oil, while the methyl esterification of the hydrolyzed products of triglycerides was treated near the supercritical methanol condition to achieve fatty acid methyl esters. Consequently, the two-step preparation was found to convert rapeseed oil to fatty acid methyl esters in considerably shorter reaction time and milder reaction condition than the direct supercritical methanol treatment. The optimum reaction condition in this two-step preparation was 270°C and 20 min for hydrolysis and methyl esterification, respectively. Variables affecting the yields in hydrolysis and methyl esterification are discussed. 

The components of biodiesel are vegetable oils composed of glycerol esters of fatty acids. In the process of transesterification, the glycerol components of the triglyceride molecules are exchanged for methanol. The products are fatty-acid methyl esters consisting of straight saturated and unsaturated hydrocarbon chains, as described under chemical processes. 

Fatty acids are obtained by fat splitting using water (hydrolysis), methanol (metha-nolysis), and base (saponification) of amines (aminolysis). Splitting with water or methanol can be considered transesterification because glycerol is liberated. The methanolysis is the reaction taking place in biodiesel production as the resulting product is called fatty acid methyl ester. 

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